1. Field of the Invention
This invention relates to a deflection yoke mounting apparatus for a color picture tube, and more particularly to a deflection yoke mounting apparatus for a color picture tube, that allows a deflection yoke to be securely fixed to a neck portion of a funnel of the picture tube to prevent deterioration of convergence and purity characteristics of the picture tube due to displacement of the yoke by an external shock.
2. Description of the Prior Art
Generally, a color picture tube has a form of a cone-shaped vacuum bulb comprising a panel (not shown) having phosphor applied in forms of dots or strips to its inner surface, and a funnel 2 integrated with the panel and having a neck portion 2a' of a reduced cross-section, as shown in FIG. 1 of the accompanying drawings. In addition, the picture tube includes an electron gun mounted internally in the neck portion 2a' to generate and direct electron beams to the phosphor of the panel, and a deflection yoke 3 fixedly mounted externally on the neck portion to deflect the electron beams.
With the color picture tube thus constructed, the electron beams emitted from the electron gun and passed through grids are deflected by the deflection yoke 3. The electron beams pass through small through-holes of a shadow mask for color selection, and then land on the phosphor of the panel to cause the luminescence of the phosphor. Thus, a picture image is formed on the screen. At this time, if a displacement of the deflection yoke occurs, convergence and purity characteristics of the picture tube may deteriorate, so that an image of good quality may not be produced. Therefore, in order to obtain an image of good quality, it is necessary to securely fix the deflection yoke 3 to the neck portion 2a' of the funnel to prevent displacement.
An example of a deflection yoke mounting apparatus for a color picture tube according to the prior art is shown in FIGS. 1, 2A, and 2B of the accompanying drawings. The deflecting yoke 3 of FIGS. 1, 2A and 2B comprises horizontal deflection coils(not shown) for correction of horizontal convergence wound into a saddle shape and disposed internally in a separator 8 of an insulating material and vertical deflection coils 7 for correction of vertical convergence round into a toroidal shape and disposed externally on the separator. The deflection yoke 3 is mounted on the neck portion 2a of the funnel through an adhesive tape 10 having on one side surface an adhesive material 9 bonded to the outer surface of the glass neck portion 2a'. More particularly, as shown in FIG. 2B, the adhesive tape 10 is first bonded around the outer periphery of the neck portion, and then a neck contact member 4 of the deflection yoke having protrusions 4a formed on its inner surface is inserted over the bonded adhesive tape and tightly clamped by a metallic band 5 wrapped around its outer periphery. The metallic band 5 is fastened by a bolt 6 which is threadedly engaged in threaded through-holes 5a formed at opposite ends of the band. As a result, the deflection yoke is fixed to the neck portion 2a' of the funnel to act against displacement.
This prior apparatus, however, has a drawback in that although the deflection yoke has been accurately assembled to the neck portion taking into consideration the convergence and purity characteristic in the manufacturing process, the yoke 3 exhibits a tendency to be displaced relative to the glass neck portion 2a' during transportation or use of the product, so that a picture image of good quality may not be obtained. In addition, during operation of the color picture tube, the temperature of the neck portion rises up to 60.degree. C..about.80.degree. C. due to heat generated by a heater of the electron gun disposed in the neck portion. As a result, the adhesive force the adhesive tape bonded to the neck portion is weakened. Thus, even a minute shock is applied to the picture tube may displace the deflection yoke thereby deteriorating the convergence or purity characteristics of the picture tube.